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Because of microbial growth limits, lowering pH is an effect…

Because of microbial growth limits, lowering pH is an effective way to preserve foods and prevent the growth of microorganisms and can also be used as a critical control point in Hazard Analysis plans. Additionally, some manufacturers adjust pH to change flavor. This is often done through pickling or fermentation. The most common way to lower pH is through fermentation. Fermentation relies on “good” bacteria to produce lactic acid, which then lowers the pH of the product and prevents the growth of other types of organisms. Pickles, sauerkraut, and olives all use this strategy. pH can also be controlled by adding acid (vinegar, lactic acid, citric acid) directly to the product, or by adding naturally acidic ingredients like tomatoes in spaghetti sauce. Table 1 shows the minimum pH limits for the growth of different types of microorganisms.  Most microorganisms stop growing at a pH of 5.0.  Some microorganisms can go as low as 4.6 and even down to 4.4. Historically, a pH of 4.6 was considered to be the lower growth limit, but portions of the food code were changed when it was discovered that some problematic microbes can grow in pH levels as low as 4.2. Table 2 shows the packing pH of several popular condiments in the grocery store. Once a condiment is opened, exposure to air causes oxidation, which increases the pH over time.  Reduced exposure to air and refrigeration slow oxidation.    Table 1. Minimum and Maximum pH limits for the growth of different types of microorganisms. Microorganism Minimum Optimum Maximum Clostridium perfringens 5.5 – 5.8 7.2 8.9 Vibrio vulnificus 5 7.8 10.2 Racillus cereus 4.9 6 – 7 8.8 Campylobacter spp. 4.9 6.5 – 7.5 9 Shigella spp. 4.9   9.3 Vibrio parahaemolyticus 4.8 7.8 – 8.6 11 Clostridium botulinum toxin 4.6   8.5 Clostridium botulinum growth 4.6   8.5 Enterohemorrhagic Escherichia coli 4.4 6 – 7 9 Listeria monocytogenes 4.39 7 9.4 Salmonella spp 4.21 7 – 7.5 9.5 Yersinia enterocolitica 4.2 7.2 9.6     Table 2.  Packing pH of Popular Condiments Bought in the Grocery Store. Type pH Strawberry Preserves 3.7 Yellow Mustard 3.6 Hot Sauce 3.6 Mediterranean Italian Dressing 3.8 Ranch Dressing 3.9   Asian Toasted Sesame Dressing 4.1   Ketchup 3.6   Mayonnaise 4.1   French Dressing 3.4   Barbecue Sauce 3.8